Helicobacter pylori is a recently recognized, Gram-negative bacillus that is found adhering to the human gastric surface mucous cells. The consensus of many clinical studies is that a high frequency of association exists between both chronic type B gastritis and duodenal ulcers and colonization by H. pylori. This project seeks to define in molecular terms the virulence mechanism(s) of H. pylori by analyzing the role of plasmid- encoded proteins in pathogenesis and by cloning the gene encoding a cytotoxin. Specifically, this study will examine clinical isolates for the presence of plasmid DNA and test the hypothesis that one or more virulence mechanisms, such as production of the cytotoxin, a mucin protease, and/or an adherence structure, are encoded on plasmid DNA. Only with an understanding of the virulence mechanism(s) of this organism can preventive measures and more effective treatments of gastric problems be developed. Participation in this project will provide MBRS students with both an understanding of and experience in the biomedical aspects of microbial and molecular biology research.